The present invention relates to the wiring structure of a semiconductor pressure sensor, more particularly, to the wiring structure of a semiconductor pressure sensor such as a medical semiconductor pressure sensor attached to the tip of a catheter in which the increase of wiring or the design of a circuit pattern is easily made.
A semiconductor pressure sensor has been developed with paying attention to the fact that when a mechanical stress is applied to a semiconductor crystal such as silicon, the resistivity of the crystal is largely changed due to the piezoresistance effect. A conventional semiconductor pressure sensor is made by forming strain gauge resistors on the surface layer of a silicon single crystal substrate by diffusion, constructing the Wheatstone bridge by wiring the four strain gauge resistors with diffused lead portions, and providing A1 pads on the diffused lead portions, and further forming an etching stop layer in the substrate so that a thin diaphragm capable of being deformed by a pressure is formed by removing the back of the silicon single crystal by etching.
The above described semiconductor pressure sensor is very small. Especially, for medical use, since a plurality of semiconductor pressure sensors are attached to the tip of a catheter which is inserted into a body, the length of a side of a chip must be about 1 mm or less even if periphery circuits such as a temperature compensation circuit are included. Further, since the sensors are disposed at the tip of the catheter, the A1 pads must be disposed at one side of the surface of the semiconductor pressure sensor, which are wired to the strain gauge resistors, sensors and the like by the diffused lead portions having a predetermined width.
The above-mentioned wiring structure with only diffused lead portions on the substrate has disadvantages that, since at least two wiring leads must be provided when an element such as a sensor or a transistor is added onto the substrate surface, other wiring leads are largely affected by the addition so that the flexibility of the design of wiring pattern, i.e., the design of circuit pattern is remarkably restricted.
Especially, the semiconductor pressure sensor for medical use is very small in chip size and the A1 pads are disposed on one side of the chip so that the design of the circuit pattern is very difficult in case that two wiring leads must be provided for the addition of an element.